Color image recording materials have now come to be the mainstream of image recording materials. Currently prevailing color image recording materials include ink-jet recording materials, electrophotographic recording materials, transfer type silver halide light-sensitive materials, printing inks, and recording pens.
These color image recording materials use colorants (including dyes and pigments) of additive or subtractive primaries to implement full color reproduction or recording. Nevertheless, colorants having absorption characteristics suitable for favorable color reproduction and fastness against various conditions of use or environmental conditions are not available for the time being. From this viewpoint, improvements have been keenly demanded.
Ink jet recording has been popularized rapidly and will see further development because of low material cost, high speed, low noise, and ease of color recording. Fundamentally, ink jet recording is divided into a continuous method in which ink droplets are continuously allowed to fly and a drop-on-demand method in which ink droplets are ejected in response to image information signals. The mechanism of drop formation includes a piezoelectric system in which pressure is applied to ink by a piezoelectric element to eject ink droplets, a thermal system in which heat is applied to ink to create bubbles whereby to eject an ink droplet, an ultrasonic system, and an electrostatic system. Ink-jet inks include aqueous ink, oily ink, and hot-melt or solid ink.
Dyes used in the ink-jet recording inks are required to have (1) good solubility or dispersibility in ink solvents, (2) capability of high-density recording, (3) satisfactory hues, (4) color fastness against light, heat, active gases in the atmosphere (e.g., Nox, oxidizing gases such as ozone, SOx, etc.), (5) resistance against water or chemicals, (6) good fixability on media with minimized feathering, (7) stability in ink formulations, (8) nontoxicity, (9) high purity, and (10) inexpensiveness. It is extremely difficult to obtain dyes that satisfy high levels of these requirements, nevertheless. In particular, there has been a strong demand for dyes with satisfactory black hue that are fast to light, humidity and heat, have a high molar absorptivity, provide high print quality in text printing, and, when used in printing a substrate having an ink receiving layer containing white, porous, inorganic pigment particles, exhibit resistance against environmental oxidizing gases such as ozone.
The following properties are required, in common, of the dyes for the above-described applications: absorption characteristics fit for color reproduction, fastness under environmental conditions, such as light, heat, humidity, and oxidizing gases (e.g., ozone), fastness against chemicals such as sulfurous acid gas, and a high molar absorptivity.
Generally used black dyes include disazo dyes and trisazo dyes. In the manufacture of the disazo and trisazo dyes, nonheterocyclic compounds, such as phenols, naphthols, naphthylamines, and anilines, are widely used as starting materials. Disazo dyes prepared from these starting materials are disclosed, e.g., in EP 761771 and Japanese Patent 2716541, but all of them are unsatisfactory in light fastness and seriously poor in fastness to oxidizing gases such as ozone in the atmosphere.
In seeking for a colorant fast to oxidizing gases such as ozone, the present inventors have reached an idea of chiefly using a heterocyclic compound in place of the conventional materials, such as phenols, naphthols, naphthylamines or anilines. Disazo and trisazo dyes that have hitherto been proposed are disclosed, e.g., in German Patent 2743097, JP-A-59-133259, and JP-A-52-76331. However, all these known dyes are those developed for dyeing fiber. The literature is silent on such performance as aimed at in the present invention, that is, whether the dye has absorption characteristics preferred for color reproduction and fastness under environmental conditions of use, such as light fastness, heat fastness, humidity fastness, fastness to chemicals (e.g., sulfurous acid gas), and, in particular, fastness to oxidizing gases, e.g., ozone. Neither does the literature give a suggestion on what structure is the most suited for image formation as contemplated in the present invention. Although JP-A-52-76331 discloses water-soluble disazo dyes containing two or more heterocyclic rings, the water-suoluble dyes turned out to have insufficient water solubility for use in ink jet applications.